Gypsum wallboard is used to construct walls and ceilings by fixing the panels to studs and filling the joints where sections are butted together with a combination of tape joint compound and perforated tape. Tape joint adhesive compositions are in two forms--powdered tape joint compounds and ready mix tape joint cement compositions. Powdered tape joint compounds are added to water and the mixture is stirred until a workable consistency is attained: whereas, ready mix compositions need only stirring before use.
In the construction industry, the ready mix tape joint cement composition is preferred for obvious convenience reasons, although both forms are used. A typical ready mix or powdered composition comprises filler components, thickeners, binders, and minor amounts of defoamer, preservative, dispersant and a processing aid to improve water-retention properties. Traditional binders include vinyl latexes of polyvinyl acetate, ethylene vinyl acetate copolymers, polyvinyl alcohol, various starches, guar gum and derivatives, casein and the like. See Elden, U.S. Pat. No. 3,303,147; Mills et al., U.S. Pat. No. 3,483,156; Wilkenson, U.S. Pat. No. 3,342,761. Binders such as polyacrylamides have also been used (Bruschtein, U.S. Pat. No. 3,793,269).
Typically, cellulose ethers are used as thickeners in adhesive compositions, more particularly in tape joint compositions. When combined with latex binders some cellulose ethers hinder bond strength properties, while others increase bond strength properties. Although in some instances cellulose ethers when combined with latex binders can increase bond strengths, this occurs when there is a large amount of the latex binder present. There are problems with using a latex binder in the adhesive compositions. The latex binders are very expensive. It has not been possible to replace the latex binder or reduce the amount used with a cellulosic thickener, such that adequate bond properties are induced in the material without excessive viscosity build-up. Obviously, it would be desirable to have a composition which has little or no latex binder present, but yet still retain good bonding and rheology properties.
In addition to the construction industry preferring the convenience of the ready mix composition, other properties such as superior thickening action, workability, open-time or water retention, crack resistance on drying, and lubricity in slip action during application are important. It would be highly desirable to have a blend of cellulose ethers that is useful in ready mix tape joint compositions, powdered tape joint compositions and other adhesive compositions. These compositions should have the properties that are desired by the construction industry, most importantly good binding properties and little or no latex binder.